Replace synthetic wrapper node approach with direct iteration fields: - ProcessorNode gains iteration (child's index) and iterationSize (container's total) fields, populated from ClickHouse flat records - Frontend hooks detect iteration containers from iterationSize != null instead of scanning for wrapper processorTypes - useExecutionOverlay filters children by iteration field instead of wrapper nodes, eliminating ITERATION_WRAPPER_TYPES entirely - Cleaner data contract: API returns exactly what the DB stores Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>